Nowadays several mobile telephone systems are known, among them the well-known GSM system. The users of the mobile phones used in this system enjoy a plurality of services, such as SMS or MMS. GPRS is a data transfer method under the GSM standard that is not dependent on call set-up.
Among all these services the Push-to-Talk (PTT) or Push-to-Talk Over Cellular (PoC) GPRS based service recently emerged.
Conventional mobile phones with PTT functionality are provided with dedicated PTT button. Basically, the method comprises pushing the PTT button, which causes a display to show the PTT phonebook in form of a list of PTT contacts. By using the up and down arrow keys, it is possible to highlight the person or person group the user want to contact. Then the user must push and hold de PTT button, and wait a period of time for a beep that confirms the connection. Next, the user can start speaking. At the other end, everyone in the person group hears a beep and then the voice of the user. When the user finishes talking, the user releases the PTT button and everyone in the person group hears another beep. The next person in the group can press his/her PTT button and can then respond. Anyone else in the group pressing their PTT button just thereafter gets a busy signal and has to wait for his/her turn.
There are mobile phones which do not have a dedicated PTT button, such as the Nokia 5140. In this case, the establishment of the connection must be done from inside of the PTT sub-menu. The user has to navigate to the PTT sub-menu and start the connection using softkeys. If the connection is established then the user has press a softkey which emulates the PTT button.
Basically, in the beginning of a PTT communication the mobile phone is in a latency state, waiting for a push of the PTT-button. When the PTT button is pushed, the mobile phone switches to an active state. When the PTT button is held, the mobile phone returns to the latency state, waiting a new activation of the PTT button.
Said PTT mobile phones have a drawback in that their use is difficult for their configuration because the user must continuously press and hold the PTT button during a PTT communication. It is very inconvenient to press a button while holding the mobile phone in a conventional position close to ear and face. Also, for example, a user cannot use a PTT mobile phone in a PTT communication when is driving a car. For the same reason it is not possible to use a hands-free headset. Another drawback is that the mobile phone must include another button in its keypad, which should though have as few keys as possible for size and ease of use considerations.